Newbie question

[richarddollet9]

Posted on May 19, 2008 at 02:09

Newbie question

[richarddollet9]

Posted on May 17, 2011 at 12:35

Hi all,

I'm just starting off playing with the STM32. First task was to toggle I/Os (PortB). It does work, but there's a tiny thing I just don't get, so I would appreciate a bit of guidance there. Why do I need to enable port B clock when it's configured as a general purpose output? RCC->APB2ENR = RCC_APB2ENR_IOPBEN; GPIOB->CRH = 0x11111111; GPIOB->ODR = 0x0000af00; It doesn't work otherwise. I understand that IDR might need it to get refreshed, but I'm wondering why it's required to drive the output ? Tks, Richard

[lanchon]

Posted on May 17, 2011 at 12:35

hi richard,

to answer that question you need the macrocell schematic and that's a secret. but you can guess, so how about this non-provable (yet disprovable) hypothesis: the macrocell requires clock to answer on the internal peripheral bus, no reads or writes to registers are possible otherwise. or this one: the macrocell is fully synchronous so no flip-flops can be updated without clock (can't write but might read regs). beyond the useful knowledge that you need the clock to use the macrocell, I can't think of a reason why you'd need the answer to your question. is there something specific you need to do or are you just curious?

[richarddollet9]

Posted on May 17, 2011 at 12:35

Hi Lanchon,

Yes it's curiosity, plus the fact that spontaneously it didn't think about enabling it. I couldn't find anything in the doc that could lead to it. I had to look into sample codes and voila. Anyway, your hypothesis does make a lot of sense to me as I was heading toward a very similar conclusion :D Tks, Richard